DESCRIPTION This research proposes to characterize the LIS1 protein with the specific goal of studying the role of the WD repeats in mediating the ability of LIS1 to form protein complexes with itself and other protein subunits. Many proteins containing WD repeats appear to participate in processes involving multi-subunit protein complexes. Previous studies within the US investigator's lab had suggested that the WD repeats in the b subunits of G proteins were important for controlling the reversible formation of G protein trimers and thus mediating the abilities of the different G protein subunits to interact with different effectors and modulating G protein function. The more recent solution of the crystal structure of the Gb subunit shows that the WD repeats participate in the formation of a seven-bladed b propeller structure and are comprised of secondary structural elements consistent with theoretical predictions made based on the analysis of a large library of WD repeat containing proteins. Initial mutagenesis studies within the US lab have tested the contributions of this seven-bladed propeller structure to various aspects of G protein function. This FIRCA application proposes to employ similar approaches to study the function of WD repeats in LIS1 function. The hypothesis being tested is that the presence of WD repeats serve a structural/function relationship common to the widely diverse group of WD-containing proteins. Specifically, the aims are: 1. To define the regions of LIS1 that specify heterodimer or homodimer formation; 2. To define the regions of LIS1 that specify trimer formation with Platelet-activating factor (PAF) acetylhydrolase (AH); 3. To map regions of LIS1 that specify interaction with microtubules by mutational analysis.